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Posted By: Richard S. Pope, PA-C, MPAS | August 20, 2019
An effusion of the knee(s) is the most common manifestation of Lyme arthritis, a late stage of infection with Borrelia burgdorferi, the tick involved in transmission. Geographically found in the East, Midwest, and now spreading into new areas, Lyme arthritis is often misdiagnosed as a nonspecific inflammatory arthritis of unknown cause.
Where I practice in Western Connecticut, the large number of adults with knee effusion in the months of January, February, and March has raised my antenna for Lyme arthritis. This is due to the 6-month delay from initial tick bite to manifestation of symptoms. The differential diagnosis of a knee effusion is large; however a high index of suspicion is needed in endemic areas.
On average, we see one to four cases annually, and it is estimated that 60% of patients not treated will develop this late complication. Occasionally, these patients will be seen in orthopedics where aspiration and corticosteroid injections are given. Although x-rays are taken and osteoarthritis is noted on the reading, the diagnosis goes undetected. The effusions return and on the second visit a Lyme titer is drawn along with other labs. The referral is made when IgG titers for Lyme on Western blot testing are positive across the IgG spectrum. Additionally, the IgM Western blot may also be positive. Inflammatory markers can be elevated, and even a false-positive rheumatoid factor can be seen.
There are several case studies in the literature where treatments with corticosteroid injections have led to prolongation of symptoms and functional decline unless appropriate antibiotic therapy is instituted. For those diagnosed with Lyme arthritis, the Infectious Disease Society of America (IDSA) guidelines recommend treatment with 28 days of oral doxycycline 100 mg twice daily. For those with continuing pain and swelling, intravenous ceftriaxone is typically infused for 14 to 28 days.
There are a few pearls and subtleties that can help alert primary care providers to this diagnosis. Many patients will have no prior personal or family history of arthritis. Usually no other joints are affected and the effusion is frequently large and most commonly in the knee. Often there is a mismatch between the size of the effusion and the relative low level of pain. However, range of joint motion and posterior popliteal swelling are quite common, and in some cases the ankle joint can be affected.
If Lyme disease is endemic where you practice, it is important to remember the time of year the case presents. Deer ticks essentially stop moving at 40 degrees Fahrenheit but do not die at lower temperatures unless there are unusual weather circumstances. Timing the stage of Lyme and new onset of knee effusion in the winter supports a tick bite that went undetected in the June/July time frame. These patients will not remember a rash or flu-like symptoms and will not recall finding or removing a tick. However, a careful history will reveal a reasonable story for exposure. If you suspect Lyme arthritis or have a case that does not resolve after antibiotic treatment, referral is recommended.
There are several disease-modifying drugs that are used for other inflammatory arthritides that can put this indolent synovitis into remission. Most cases resolve with initial antibiotic treatment and only a small percent will need disease-modifying therapy. Long-term antibiotic therapy is not recommended by the IDSA and many other medical organizations.
- Cameron DJ. Consequences of treatment delay in Lyme disease. J Eval Clin Pract. 2007;13:470-472.
- Centers for Disease Control and Prevention. Lyme disease. www.cdc.gov/lyme/datasurveillance/index.html. Accessed August 15, 2019.
- Steere AC, Schoen RT, Taylor E. The clinical evolution of Lyme arthritis. Ann Intern Med. 1987;107:725-731.
- Wormser GP, Dattwyler RJ, Shapiro ED, et al. The clinical assessment, treatment, and prevention of Lyme disease, human granulocytic anaplasmosis, and babesiosis: clinical practice guidelines by the Infectious Diseases Society of America. Clin Infect Dis. 2006;43:1089-1134.